The general objective of the present research is to provide data on the temporal and spectral components of children's functional misarticulation of the /s/ sound. Two related objectives in this investigation are: 1) to measure those components of misarticulated /s/ at fixed intervals over a substantial period of time, and thus describe more precisely the changes that might occur during 'normal' mastery of a speech sound, and 2) to measure these components of misarticulated /s/ as a function of clinical intervention, that is, training a child to 'shape' a correct /s/ sound. Three experiments are described which are intended to meet these objectives. Experiment I is designed to provide the general descriptive data, and includes a group of ten children aged 4.0-6.0 years who do not misarticulate /s/. A speech sample of mono- and bisyllabic forms is developed in which the /s/ sound is varied according to position-in-word and several aspects of phonetic context. Children produce multiple samples of each item, and recordings of all speech samples are made under laboratory conditions. Spectrographic and real-time wave analyzer techniques are used to derive the duration and spectral data, respectively. Experiments II and III use children from the misarticulating group only, and focus on changing patterns of the temporal and spectral aspects of /s/ production. Experiment II follows experiment I in time, and obtains /s/-production data during the time when the child is being trained to produce a correct /s/. Data from experiments II and III are compared to assess the effects of normal development versus intervention on patterns of change in /s/-duration and spectra.